Dave Jones

add another block to the inside skin and have a normal gutter. box gutters = ongoing maintenance every year, clearing moss/leaves. it wont be the architect who does that.

have you got MVHR or trickle vents ? ICF should be very good for no leakage would have thought. Whats your heating req in m2 in watts ? gut feeling is your 50% overspeccing the ashp. it should never have to run a defrost cycle if used properly. mine never has.

drill baby drill. Reform will sort.

remove all zoning controls (if any fitted), 8kw sounds very large, what do the heat loss calcs say the engineer has provided to you backing up his design of 8kw being required ?

i tried also, octopus refused without MCS cert. How did you manage it ?

the problem with self install is no MCS paperwork. Octopus wouldnt accept any export from me (for payment) without it.

thats a cold roof not a warm roof. warm roof has to be sealed and doesnt require ventilation. very difficult to achieve by insulating between rafters on the underside.

car charger (not a piece of paper) is a planning requirement for us. It has to be a proper charger not a socket.

we have 150 in our airtight place. adding the celotex as well would be pointless honestly. The heat pump spins 4 hours max overnight at -10c already. 250m2. save yourself a load of time and hassle and invest in better windows and doors.

did our last 2 builds on a notice. cheaper than paying an architect for plans that only BCO will look at and file. The flip side you need to know what your doing so not good for a noobie. At least you have the archi to blame/sue if it goes wrong.

existing is more of a challenge where there is none/not enough cavity insulation. Compromise is EWI with doggo render or smaller rooms and internal. Damp being major side effect of poor install would defiantly have networked decentralised MVHR units to take care of any potential issues where there is no room for ducting a normal system.

you wont pass building control inspection if your cold roof isnt correctly vented. The tyvec at ridge needs cutting out as it will be overlapped with dry kit for the ridge. eggboxes at eaves where cavity insulation is covered by loft roll etc. you can only get condensation if heat is escaping into the loft, 400mm min of loftroll everywhere and no probs. Forget using loft as storage.

put a dergo in as well. sign it off. remove vent pipe from roof. If you have a combined foul and grey sewer then the downpipes are venting it anyway although it doesnt appear to be an 'approved' method for reasons only understandable by building control.

they wont touch it. its a closed con shop the MCS system. They will want to have done all the work and charged you 5x the market rates.

out of curiosity why are you going down the #TF route ? Are you expecting to be fully complete in 3 months and move in ? speed seems to be the only factor in justifying its double the cost of a normal build.